The present invention relates to interfolding apparatuses, and more specifically to the transfer of sheets onto interfolding rolls of the interfolding apparatuses.
Various combinations and types of rolls can be present in an interfolding apparatus. A typical interfolding apparatus includes at least two interfolding rolls, at least one knife or cutting roll, and at least one feed roll for pulling streams of web material into the interfolding apparatus. The web material is generally cut at or near the knife rolls and is eventually transferred to a nip between the interfolding rolls.
The succession of sheets entering the nip is such that a middle portion of a reference sheet on a first interfolding roll enters the nip at the same time as trailing and leading edges of downstream and upstream sheets, respectively, positioned on a second interfolding roll. The leading and trailing edges are positioned adjacent a tucker of the second interfolding roll. The tucker pushes or tucks the middle portion of the reference sheet into a gripper (either mechanical or vacuum) of the first interfolding roll as the tucker and gripper pass through the nip. The gripper receives the middle portion and the trailing and leading edges from the tucker, folds the middle portion capturing the leading and trailing edges within the fold, and conveys and releases the fold to an adjacent side of a stack of interfolded sheets being built below the interfolding rolls. As the interfolding rolls continue rotation, a gripper of the second interfolding roll receives a middle portion of the upstream sheet and the associated leading and trailing edges from a tucker of the first interfolding roll, folds the middle portion capturing the associated leading and trailing edges, and conveys and releases the fold to the adjacent side of the stack of interfolded sheets.
This process is repeated in an alternating fashion between the first and second interfolding rolls. To insure that the associated leading and trailing edges are properly folded within the middle portion of the sheet being folded, it is important to control the position of the leading and trailing edges on the interfolding rolls, and more particularly relative to the tucker of the interfolding roll.
Known interfolders attempt to maintain the position of the leading and trailing edges during interfolding by providing vacuum ports on the interfolding rolls. However, during interfolding as described above, a tucker forces a middle portion of a sheet into a recess of an opposite gripper. The length of sheet forced within the gripper must be compensated for by stretch or rupture of the sheet or by movement of one, or both, of the leading and trailing edges of the sheet being folded. In some cases, this will alter the position of the leading edge (i.e., draw it closer to the middle portion) such that the leading edge is pulled from the downstream gripper which performed the previous fold. In other cases, this will alter the position of the trailing edge such that the trailing edge is pulled from its respective vacuum port. In some extreme cases, tucking a middle portion of a sheet within an opposite gripper will cause the trailing edge of the sheet being folded to become freed from the gripper or the leading edge to become freed from the vacuum port. Where an edge moves or becomes freed, the edge is not tucked tightly within the fold and a visible discontinuity in the stack could result. In the case of a freed edge, interruption of the interfolding could occur.